A dissolved substance can exist in two forms, X and Y.
X(aq)⇌Y(aq) \mathrm{X(aq) \rightleftharpoons Y(aq)} X(aq)⇌Y(aq)X is colourless and Y is orange.
Two identical sealed flasks initially contain equal masses of pure X dissolved in equal volumes of water. The flasks are otherwise treated identically, but they are kept at different temperatures until equilibrium is reached.
| Temperature / °C | Percentage of X and Y present that is Y by mass (%) |
|---|---|
| 20 | 24 |
| 70 | 79 |
The equilibrium mixture at 70 °C is then cooled to 20 °C. All other conditions remain unchanged.
Explain what the results show about the energy change of the forward reaction and what happens to the appearance of the mixture when it is cooled.
124 exam-style questions on OCR GCSE Chemistry 5.3 Equilibria, covering 5.3.1 Reversible reactions and dynamic equilibrium and 5.3.2 Changing the position of equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.